The present invention relates generally to apparatuses for making intercell welds in electric storage batteries, and more particularly, to those apparatuses where electrodes are oriented on either side of a partition or other aperture in a battery case, lugs or other battery parts are placed over such side of that aperture, contact produced therebetween, current passed through the lead parts to melt the same and pressure applied generally for the purpose of providing an electrical connection through the aperture. Such an apparatus is shown in U.S. Pat. No. 4,013,864.
It has long been known that lead parts on either side of a partition with an aperture formed therein can be welded through that aperture using any one of a number of techniques. In the lead acid battery art, the most common site for welding lead through an aperture is during the formation of intercell connections, that is, in making the electrical connections between one battery cell and the next and/or between the endmost battery cells and the exterior battery terminal of the battery. Since connections through apertures of this sort, in addition to being electrical, must provide a liquid seal from cell to cell to prevent "pumping", some attention has been directed in the art concerning various methods for insuring that an intercell connector, in addition to providing a good electrical connection, will also exhibit good sealing characteristics.
U.S. Pat. No. 3,687,734 generally discloses a connector for electrically connecting two elements of a storage battery through an aperture wherein at least one of the connector lugs is provided with a passage extending therethrough. Molten material from an internal portion of the connector exits through this passage during the heat fusion step as a result of pressure from a heat energy build-up. The patentee attempts by this structure to avoid the problem of blow-outs or lead expulsion which has been encountered by many practitioners in this art.
Another attempt to avoid "blow-out" is disclosed in U.S. Pat. No. 3,476,611 wherein intercell connections are made by a projection welding process from pins which extend through the partition between two adjacent battery compartments, which pins have dimensions such that, when they are fluidized during the process, the volume of the pin material does not exceed the volume defined by the walls of the opening.
Such attempts inherently involve tolerance and positioning problems during manufacture and assembly of the parts and battery. More recently, other methods have been developed for producing battery intercell electrical connections, which methods have generally been referred to as "extrusion-fusion" type methods. For example, in U.S. Pat. No. 3,793,086 a method is disclosed wherein flat surfaced connector lugs are placed on each side of the battery partition wall, adjacent an aperture. The connector lugs are extruded by a pair of opposed electrodes into the aperture until they meet, whereupon an electrical welding circuit is applied. When the welding current ceases, the connector is allowed to cool. U.S. Pat. No. 3,793,086 states:
"It should be emphasized that reduction of the initially applied shear force during the welding cycle is essential. If the high applied shear force is maintained during the welding cycle, molten lead will be squirted from the welding joint and an imperfect joint can result."
Another approach to the problem of blow-outs is that disclosed, for example, in Canadian Pat. No. 973,522 wherein separate hold-down sleeves are employed to clamp the lugs into sealing engagement with the partition wall aperture prior to and during the extrusion-fusion process.
In U.S. Patent application Ser. No. 134,442, filed Apr. 15, 1971, referred to in U.S. Pat. No. 3,869,316, a similar process is disclosed wherein two thick plate strap lugs are clamped tightly against an intercell partition having an aperture in it, metal is extruded until contact is made, electric current is passed through the extruded metal to melt it, and, under the continuing force of the electrodes, metal is caused to flow into any voids in the aperture while, at the same time, extruding more metal out of the lugs into the aperture until the aperture is packed full of lug metal.
In U.S. Pat. No. 3,869,316 a similar extrusion-fusion system is disclosed wherein high density polyurethane pads are provided around each of the electrodes to clamp the lugs tightly against the walls of the intercell connection during the extrusion, fusion and cooling steps.
In U.S. Pat. No. 3,723,699 the problem of blow-outs or lead expulsion is expressed in a projection welding context wherein the lugs are provided with upstanding annular ribs which surround the hole in the partition wall and are caused to bite into the partition wall, in an attempt to minimize unwanted flow and providing a good mechanical key between the lugs and partition wall, thus minimizing the possibility of relative sliding movement between the lugs and partition wall.
Accordingly, as seen from the above-described prior art references, considerable problems have been experienced with blow-outs, particularly where lead is extruded into the aperture of the partition with the intent of filling the same. Extrusion-fusion welding processes have nonetheless achieved considerable success in the industry.